Method for coding image on basis of deblocking filtering, and apparatus therefor

ABSTRACT

A method for decoding an image, according to the present document, comprises: receiving a bitstream including BDPCM information; deriving residual samples for a current block on the basis of the BDPCM information; deriving prediction samples for the current block on the basis of the BDPCM information; generating a reconstructed picture on the basis of the residual samples and the prediction samples; and performing deblocking filtering on the reconstructed picture, wherein when BDPCM is applied to the current block, the deblocking filtering is not performed.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure relates to a video coding technique and, moreparticularly, to a video coding method based on deblocking filtering ina video coding system and the apparatus for the same.

Related Art

Nowadays, the demand for high-resolution and high-quality images/videossuch as 4K, 8K or more ultra high definition (UHD) images/videos hasbeen increasing in various fields. As the image/video data becomeshigher resolution and higher quality, the transmitted information amountor bit amount increases as compared to the conventional image data.Therefore, when image data is transmitted using a medium such as aconventional wired/wireless broadband line or image/video data is storedusing an existing storage medium, the transmission cost and the storagecost thereof are increased.

Further, nowadays, the interest and demand for immersive media such asvirtual reality (VR), artificial reality (AR) content or hologram, orthe like is increasing, and broadcasting for images/videos having imagefeatures different from those of real images, such as a game image isincreasing.

Accordingly, there is a need for a highly efficient image/videocompression technique for effectively compressing and transmitting orstoring, and reproducing information of high resolution and high qualityimages/videos having various features as described above.

SUMMARY

A technical aspect of the present disclosure is to provide a method andan apparatus for increasing image coding efficiency.

The present disclosure also provides a method and apparatus forincreasing efficiency of transform index coding in video coding based ondeblocking filtering.

The present disclosure also provides a method and apparatus fordeblocking filtering for a video which is coded based on a BDPCM.

The present disclosure also provides a video coding method and apparatusfor a chroma component which is coded based on a BDPCM.

In an aspect, a video decoding method performed by a decoding apparatusis provided. The method may include receiving a bitstream includingBDPCM (block differential pulse coded modulation or Block-based DeltaPulse Code Modulation) information; deriving residual samples for acurrent block based on the BDPCM information; deriving predictionsamples for the current block based on the BDPCM information; generatinga reconstructed picture based on the residual sample and the predictionsample; performing deblocking filtering on the reconstructed picture,wherein, when a BDPCM is applied to the current block, the deblockingfiltering may not be performed.

The BDPCM information may include flag information that indicateswhether the BDPCM is applied to the current block, and when the flaginformation is 1, a boundary strength (bS) for the deblocking filteringmay be derived as zero.

The current block may include a luma coding block or a chroma codingblock.

A tree type of the current block may be a single tree type, the currentblock may be the chroma coding block, and when the flag information is1, the boundary strength may be derived as 1.

The step of deriving the residual samples may include deriving aquantized transform coefficient for the current block based on theBDPCM; and deriving a transform coefficient by performing dequantizationof the quantized transform coefficient.

The quantized transform coefficient may be derived based on directionalinformation for a direction in which the BDPCM is performed.

An intra prediction sample for the current block may be derived based ona direction in which the BDPCM is performed.

In another aspect, a video encoding method performed by an encodingapparatus is provided. The method may include deriving predictionsamples for a current block based on a BDPCM (block differential pulsecoded modulation or Block-based Delta Pulse Code Modulation); derivingresidual samples for the current block based on the prediction samples;generating a reconstructed picture based on the residual sample and theprediction sample; performing deblocking filtering on the reconstructedpicture; deriving quantized residual information for a current blockbased on the BDPCM; and encoding the quantized residual information andBDPCM information for the BDPCM, wherein, when the BDPCM is applied tothe current block, the deblocking filtering may not be performed.

According to still another embodiment of the present disclosure, theremay be provided a digital storage medium that stores image dataincluding encoded image information and a bitstream generated accordingto an image encoding method performed by an encoding apparatus.

According to yet another embodiment of the present disclosure, there maybe provided a digital storage medium that stores image data includingencoded image information and a bitstream to cause a decoding apparatusto perform the image decoding method.

Advantageous Effects

According to the present disclosure, it is possible to increase overallimage/video compression efficiency.

According to the present disclosure, the efficiency of deblockingfiltering in video coding based on a BDPCM may be increased.

According to the present disclosure, the efficiency of deblockingfiltering of a chroma image based on a BDPCM may be increased.

The effects that can be obtained through specific examples of thepresent disclosure are not limited to the effects listed above. Forexample, there may be various technical effects that a person havingordinary skill in the related art can understand or derive from thepresent disclosure. Accordingly, specific effects of the presentdisclosure are not limited to those explicitly described in the presentdisclosure and may include various effects that can be understood orderived from the technical features of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an example of a video/image codingsystem to which the present disclosure is applicable.

FIG. 2 is a diagram schematically illustrating a configuration of avideo/image encoding apparatus to which the present disclosure isapplicable.

FIG. 3 is a diagram schematically illustrating a configuration of avideo/image decoding apparatus to which the present disclosure isapplicable.

FIG. 4 is a control flowchart for describing a deblocking filteringprocedure according to an embodiment.

FIG. 5 is a diagram illustrating samples located at a boundary of ablock.

FIG. 6 is a diagram illustrating a method for determining a bS accordingto an embodiment of the present disclosure.

FIG. 7 is a control flowchart for describing a video decoding methodaccording to an embodiment of the present disclosure.

FIG. 8 is a control flowchart for describing a video encoding methodaccording to an embodiment of the present disclosure.

FIG. 9 illustrates the structure of a content streaming system to whichthe present disclosure is applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

While the present disclosure may be susceptible to various modificationsand include various embodiments, specific embodiments thereof have beenshown in the drawings by way of example and will now be described indetail. However, this is not intended to limit the present disclosure tothe specific embodiments disclosed herein. The terminology used hereinis for the purpose of describing specific embodiments only, and is notintended to limit technical idea of the present disclosure. The singularforms may include the plural forms unless the context clearly indicatesotherwise. The terms such as “include” and “have” are intended toindicate that features, numbers, steps, operations, elements,components, or combinations thereof used in the following descriptionexist, and thus should not be understood as that the possibility ofexistence or addition of one or more different features, numbers, steps,operations, elements, components, or combinations thereof is excluded inadvance.

Meanwhile, each component on the drawings described herein isillustrated independently for convenience of description as tocharacteristic functions different from each other, and however, it isnot meant that each component is realized by a separate hardware orsoftware. For example, any two or more of these components may becombined to form a single component, and any single component may bedivided into plural components. The embodiments in which components arecombined and/or divided will belong to the scope of the patent right ofthe present disclosure as long as they do not depart from the essence ofthe present disclosure.

Hereinafter, preferred embodiments of the present disclosure will beexplained in more detail while referring to the attached drawings. Inaddition, the same reference signs are used for the same components onthe drawings, and repeated descriptions for the same components will beomitted.

This document relates to video/image coding. For example, themethod/example disclosed in this document may relate to a VVC (VersatileVideo Coding) standard (ITU-T Rec. H.266), a next-generation video/imagecoding standard after VVC, or other video coding related standards(e.g., HEVC (High Efficiency Video Coding) standard (ITU-T Rec. H.265),EVC (essential video coding) standard, AVS2 standard, etc.).

In this document, a variety of embodiments relating to video/imagecoding may be provided, and, unless specified to the contrary, theembodiments may be combined to each other and be performed.

In this document, a video may mean a set of a series of images overtime. Generally a picture means a unit representing an image at aspecific time zone, and a slice/tile is a unit constituting a part ofthe picture. The slice/tile may include one or more coding tree units(CTUs). One picture may be constituted by one or more slices/tiles. Onepicture may be constituted by one or more tile groups. One tile groupmay include one or more tiles.

A pixel or a pel may mean a smallest unit constituting one picture (orimage). Also, ‘sample’ may be used as a term corresponding to a pixel. Asample may generally represent a pixel or a value of a pixel, and mayrepresent only a pixel/pixel value of a luma component or only apixel/pixel value of a chroma component. Alternatively, the sample mayrefer to a pixel value in the spatial domain, or when this pixel valueis converted to the frequency domain, it may refer to a transformcoefficient in the frequency domain.

A unit may represent the basic unit of image processing. The unit mayinclude at least one of a specific region and information related to theregion. One unit may include one luma block and two chroma (e.g., cb,cr) blocks. The unit and a term such as a block, an area, or the likemay be used in place of each other according to circumstances. In ageneral case, an M×N block may include a set (or an array) of samples(or sample arrays) or transform coefficients consisting of M columns andN rows.

In this document, the term “I” and “,” should be interpreted to indicate“and/or.” For instance, the expression “A/B” may mean “A and/or B.”Further, “A, B” may mean “A and/or B.” Further, “A/B/C” may mean “atleast one of A, B, and/or C.” Also, “A/B/C” may mean “at least one of A,B, and/or C.”

Further, in the document, the term “or” should be interpreted toindicate “and/or.” For instance, the expression “A or B” may include 1)only A, 2) only B, and/or 3) both A and B. In other words, the term “or”in this document should be interpreted to indicate “additionally oralternatively.”

In the present disclosure, “at least one of A and B” may mean “only A”,“only B”, or “both A and B”. In addition, in the present disclosure, theexpression “at least one of A or B” or “at least one of A and/or B” maybe interpreted as “at least one of” A and B.

In addition, in the present disclosure, “at least one of A, B, and C”may mean “only A”, “only B”, “only C”, or “any combination of A, B, andC”. In addition, “at least one of A, B, or C” or “at least one of A, B,and/or C” may mean “at least one of” A, B, and C.

In addition, a parenthesis used in the present disclosure may mean “forexample”. Specifically, when indicated as “prediction (intraprediction)”, it may mean that “intra prediction” is proposed as anexample of “prediction”. In other words, the “prediction” of the presentdisclosure is not limited to “intra prediction”, and “intra prediction”may be proposed as an example of “prediction”. In addition, whenindicated as “prediction (i.e., intra prediction)”, it may also meanthat “intra prediction” is proposed as an example of “prediction”.

Technical features individually described in one figure in the presentdisclosure may be individually implemented or may be simultaneouslyimplemented.

FIG. 1 schematically illustrates an example of a video/image codingsystem to which the present disclosure is applicable.

Referring to FIG. 1, the video/image coding system may include a firstdevice (source device) and a second device (receive device). The sourcedevice may deliver encoded video/image information or data in the formof a file or streaming to the receive device via a digital storagemedium or network.

The source device may include a video source, an encoding apparatus, anda transmitter. The receive device may include a receiver, a decodingapparatus, and a renderer. The encoding apparatus may be called avideo/image encoding apparatus, and the decoding apparatus may be calleda video/image decoding apparatus. The transmitter may be included in theencoding apparatus. The receiver may be included in the decodingapparatus. The renderer may include a display, and the display may beconfigured as a separate device or an external component.

The video source may obtain a video/image through a process ofcapturing, synthesizing, or generating a video/image. The video sourcemay include a video/image capture device and/or a video/image generatingdevice. The video/image capture device may include, for example, one ormore cameras, video/image archives including previously capturedvideo/images, or the like. The video/image generating device mayinclude, for example, a computer, a tablet and a smartphone, and may(electronically) generate a video/image. For example, a virtualvideo/image may be generated through a computer or the like. In thiscase, the video/image capturing process may be replaced by a process ofgenerating related data.

The encoding apparatus may encode an input video/image. The encodingapparatus may perform a series of procedures such as prediction,transform, and quantization for compression and coding efficiency. Theencoded data (encoded video/image information) may be output in the formof a bitstream.

The transmitter may transmit the encoded video/image information or dataoutput in the form of a bitstream to the receiver of the receive devicethrough a digital storage medium or a network in the form of a file orstreaming. The digital storage medium may include various storagemediums such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. Thetransmitter may include an element for generating a media file through apredetermined file format, and may include an element for transmissionthrough a broadcast/communication network. The receiver mayreceive/extract the bitstream and transmit the received/extractedbitstream to the decoding apparatus.

The decoding apparatus may decode a video/image by performing a seriesof procedures such as dequantization, inverse transform, prediction, andthe like corresponding to the operation of the encoding apparatus.

The renderer may render the decoded video/image. The renderedvideo/image may be displayed through the display.

FIG. 2 is a diagram schematically illustrating a configuration of avideo/image encoding apparatus to which the present disclosure isapplicable. Hereinafter, what is referred to as the video encodingapparatus may include an image encoding apparatus.

Referring to FIG. 2, the encoding apparatus 200 may include an imagepartitioner 210, a predictor 220, a residual processor 230, an entropyencoder 240, an adder 250, a filter 260, and a memory 270. The predictor220 may include an inter predictor 221 and an intra predictor 222. Theresidual processor 230 may include a transformer 232, a quantizer 233, adequantizer 234, an inverse transformer 235. The residual processor 230may further include a subtractor 231. The adder 250 may be called areconstructor or reconstructed block generator. The image partitioner210, the predictor 220, the residual processor 230, the entropy encoder240, the adder 250, and the filter 260, which have been described above,may be constituted by one or more hardware components (e.g., encoderchipsets or processors) according to an embodiment. Further, the memory270 may include a decoded picture buffer (DPB), and may be constitutedby a digital storage medium. The hardware component may further includethe memory 270 as an internal/external component.

The image partitioner 210 may partition an input image (or a picture ora frame) input to the encoding apparatus 200 into one or more processingunits. As one example, the processing unit may be called a coding unit(CU). In this case, starting with a coding tree unit (CTU) or thelargest coding unit (LCU), the coding unit may be recursivelypartitioned according to the Quad-tree binary-tree ternary-tree (QTBTTT)structure. For example, one coding unit may be divided into a pluralityof coding units of a deeper depth based on the quad-tree structure, thebinary-tree structure, and/or the ternary structure. In this case, forexample, the quad-tree structure may be applied first and thebinary-tree structure and/or the ternary structure may be applied later.Alternatively, the binary-tree structure may be applied first. Thecoding procedure according to the present disclosure may be performedbased on the final coding unit which is not further partitioned. In thiscase, the maximum coding unit may be used directly as a final codingunit based on coding efficiency according to the image characteristic.Alternatively, the coding unit may be recursively partitioned intocoding units of a further deeper depth as needed, so that the codingunit of an optimal size may be used as a final coding unit. Here, thecoding procedure may include procedures such as prediction, transform,and reconstruction, which will be described later. As another example,the processing unit may further include a prediction unit (PU) or atransform unit (TU). In this case, the prediction unit and the transformunit may be split or partitioned from the above-described final codingunit. The prediction unit may be a unit of sample prediction, and thetransform unit may be a unit for deriving a transform coefficient and/ora unit for deriving a residual signal from a transform coefficient.

The unit and a term such as a block, an area, or the like may be used inplace of each other according to circumstances. In a general case, anM×N block may represent a set of samples or transform coefficientsconsisting of M columns and N rows. The sample may generally represent apixel or a value of a pixel, and may represent only a pixel/pixel valueof a luma component, or only a pixel/pixel value of a chroma component.The sample may be used as a term corresponding to a pixel or a pel ofone picture (or image).

The subtractor 231 subtractes a prediction signal (predicted block,prediction sample array) output from the predictor 220 from an inputimage signal (original block, original sample array) to generate aresidual signal (residual block, residual sample array), and thegenerated residual signal is transmitted to the transformer 232. Thepredictor 220 may perform prediction on a processing target block(hereinafter, referred to as ‘current block’), and may generate apredicted block including prediction samples for the current block. Thepredictor 220 may determine whether intra prediction or inter predictionis applied on a current block or CU basis. As discussed later in thedescription of each prediction mode, the predictor may generate variousinformation relating to prediction, such as prediction mode information,and transmit the generated information to the entropy encoder 240. Theinformation on the prediction may be encoded in the entropy encoder 240and output in the form of a bitstream.

The intra predictor 222 may predict the current block by referring tosamples in the current picture. The referred samples may be located inthe neighbor of or apart from the current block according to theprediction mode. In the intra prediction, prediction modes may include aplurality of non-directional modes and a plurality of directional modes.The non-directional modes may include, for example, a DC mode and aplanar mode. The directional mode may include, for example, 33directional prediction modes or 65 directional prediction modesaccording to the degree of detail of the prediction direction. However,this is merely an example, and more or less directional prediction modesmay be used depending on a setting. The intra predictor 222 maydetermine the prediction mode applied to the current block by using theprediction mode applied to the neighboring block.

The inter predictor 221 may derive a predicted block for the currentblock based on a reference block (reference sample array) specified by amotion vector on a reference picture. At this time, in order to reducethe amount of motion information transmitted in the inter predictionmode, the motion information may be predicted on a block, subblock, orsample basis based on correlation of motion information between theneighboring block and the current block. The motion information mayinclude a motion vector and a reference picture index. The motioninformation may further include inter prediction direction (L0prediction, L1 prediction, Bi prediction, etc.) information. In the caseof inter prediction, the neighboring block may include a spatialneighboring block existing in the current picture and a temporalneighboring block existing in the reference picture. The referencepicture including the reference block and the reference pictureincluding the temporal neighboring block may be same to each other ordifferent from each other. The temporal neighboring block may be calleda collocated reference block, a collocated CU (colCU), and the like, andthe reference picture including the temporal neighboring block may becalled a collocated picture (colPic). For example, the inter predictor221 may configure a motion information candidate list based onneighboring blocks and generate information indicating which candidateis used to derive a motion vector and/or a reference picture index ofthe current block. Inter prediction may be performed based on variousprediction modes. For example, in the case of a skip mode and a mergemode, the inter predictor 221 may use motion information of theneighboring block as motion information of the current block. In theskip mode, unlike the merge mode, the residual signal may not betransmitted. In the case of the motion information prediction (motionvector prediction, MVP) mode, the motion vector of the neighboring blockmay be used as a motion vector predictor and the motion vector of thecurrent block may be indicated by signaling a motion vector difference.

The predictor 220 may generate a prediction signal based on variousprediction methods. For example, the predictor may apply intraprediction or inter prediction for prediction on one block, and, aswell, may apply intra prediction and inter prediction at the same time.This may be called combined inter and intra prediction (CIIP). Further,the predictor may be based on an intra block copy (IBC) prediction mode,or a palette mode in order to perform prediction on a block. The IBCprediction mode or palette mode may be used for content image/videocoding of a game or the like, such as screen content coding (SCC).Although the IBC basically performs prediction in a current block, itcan be performed similarly to inter prediction in that it derives areference block in a current block. That is, the IBC may use at leastone of inter prediction techniques described in the present disclosure.

The prediction signal generated through the inter predictor 221 and/orthe intra predictor 222 may be used to generate a reconstructed signalor to generate a residual signal. The transformer 232 may generatetransform coefficients by applying a transform technique to the residualsignal. For example, the transform technique may include at least one ofa discrete cosine transform (DCT), a discrete sine transform (DST), aKarhunen-Loeve transform (KLT), a graph-based transform (GBT), or aconditionally non-linear transform (CNT). Here, the GBT means transformobtained from a graph when relationship information between pixels isrepresented by the graph. The CNT refers to transform obtained based ona prediction signal generated using all previously reconstructed pixels.In addition, the transform process may be applied to square pixel blockshaving the same size or may be applied to blocks having a variable sizerather than the square one.

The quantizer 233 may quantize the transform coefficients and transmitthem to the entropy encoder 240, and the entropy encoder 240 may encodethe quantized signal (information on the quantized transformcoefficients) and output the encoded signal in a bitstream. Theinformation on the quantized transform coefficients may be referred toas residual information. The quantizer 233 may rearrange block typequantized transform coefficients into a one-dimensional vector formbased on a coefficient scan order, and generate information on thequantized transform coefficients based on the quantized transformcoefficients of the one-dimensional vector form. The entropy encoder 240may perform various encoding methods such as, for example, exponentialGolomb, context-adaptive variable length coding (CAVLC),context-adaptive binary arithmetic coding (CABAC), and the like. Theentropy encoder 240 may encode information necessary for video/imagereconstruction other than quantized transform coefficients (e.g. valuesof syntax elements, etc.) together or separately. Encoded information(e.g., encoded video/image information) may be transmitted or stored ona unit basis of a network abstraction layer (NAL) in the form of abitstream. The video/image information may further include informationon various parameter sets such as an adaptation parameter set (APS), apicture parameter set (PPS), a sequence parameter set (SPS), a videoparameter set (VPS) or the like. Further, the video/image informationmay further include general constraint information. In the presentdisclosure, information and/or syntax elements which aretransmitted/signaled to the decoding apparatus from the encodingapparatus may be included in video/image information. The video/imageinformation may be encoded through the above-described encodingprocedure and included in the bitstream. The bitstream may betransmitted through a network, or stored in a digital storage medium.Here, the network may include a broadcast network, a communicationnetwork and/or the like, and the digital storage medium may includevarious storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, andthe like. A transmitter (not shown) which transmits a signal output fromthe entropy encoder 240 and/or a storage (not shown) which stores it maybe configured as an internal/external element of the encoding apparatus200, or the transmitter may be included in the entropy encoder 240.

Quantized transform coefficients output from the quantizer 233 may beused to generate a prediction signal. For example, by applyingdequantization and inverse transform to quantized transform coefficientsthrough the dequantizer 234 and the inverse transformer 235, theresidual signal (residual block or residual samples) may bereconstructed. The adder 155 adds the reconstructed residual signal to aprediction signal output from the inter predictor 221 or the intrapredictor 222, so that a reconstructed signal (reconstructed picture,reconstructed block, reconstructed sample array) may be generated. Whenthere is no residual for a processing target block as in a case wherethe skip mode is applied, the predicted block may be used as areconstructed block. The adder 250 may be called a reconstructor or areconstructed block generator. The generated reconstructed signal may beused for intra prediction of a next processing target block in thecurrent block, and as described later, may be used for inter predictionof a next picture through filtering.

Meanwhile, in the picture encoding and/or reconstructing process, lumamapping with chroma scaling (LMCS) may be applied.

The filter 260 may improve subjective/objective video quality byapplying the filtering to the reconstructed signal. For example, thefilter 260 may generate a modified reconstructed picture by applyingvarious filtering methods to the reconstructed picture, and may storethe modified reconstructed picture in the memory 270, specifically inthe DPB of the memory 270. The various filtering methods may include,for example, deblocking filtering, sample adaptive offset, an adaptiveloop filter, a bilateral filter or the like. As discussed later in thedescription of each filtering method, the filter 260 may generatevarious information relating to filtering, and transmit the generatedinformation to the entropy encoder 240. The information on the filteringmay be encoded in the entropy encoder 240 and output in the form of abitstream.

The modified reconstructed picture which has been transmitted to thememory 270 may be used as a reference picture in the inter predictor221. Through this, the encoding apparatus can avoid prediction mismatchin the encoding apparatus 100 and a decoding apparatus when the interprediction is applied, and can also improve coding efficiency.

The memory 270 DPB may store the modified reconstructed picture in orderto use it as a reference picture in the inter predictor 221. The memory270 may store motion information of a block in the current picture, fromwhich motion information has been derived (or encoded) and/or motioninformation of blocks in an already reconstructed picture. The storedmotion information may be transmitted to the inter predictor 221 to beutilized as motion information of a neighboring block or motioninformation of a temporal neighboring block. The memory 270 may storereconstructed samples of reconstructed blocks in the current picture,and transmit them to the intra predictor 222.

FIG. 3 is a diagram schematically illustrating a configuration of avideo/image decoding apparatus to which the present disclosure isapplicable.

Referring to FIG. 3, the video decoding apparatus 300 may include anentropy decoder 310, a residual processor 320, a predictor 330, an adder340, a filter 350 and a memory 360. The predictor 330 may include aninter predictor 331 and an intra predictor 332. The residual processor320 may include a dequantizer 321 and an inverse transformer 321. Theentropy decoder 310, the residual processor 320, the predictor 330, theadder 340, and the filter 350, which have been described above, may beconstituted by one or more hardware components (e.g., decoder chipsetsor processors) according to an embodiment. Further, the memory 360 mayinclude a decoded picture buffer (DPB), and may be constituted by adigital storage medium. The hardware component may further include thememory 360 as an internal/external component.

When a bitstream including video/image information is input, thedecoding apparatus 300 may reconstruct an image correspondingly to aprocess by which video/image information has been processed in theencoding apparatus of FIG. 2. For example, the decoding apparatus 300may derive units/blocks based on information relating to block partitionobtained from the bitstream. The decoding apparatus 300 may performdecoding by using a processing unit applied in the encoding apparatus.Therefore, the processing unit of decoding may be, for example, a codingunit, which may be partitioned along the quad-tree structure, thebinary-tree structure, and/or the ternary-tree structure from a codingtree unit or a largest coding unit. One or more transform units may bederived from the coding unit. And, the reconstructed image signaldecoded and output through the decoding apparatus 300 may be reproducedthrough a reproducer.

The decoding apparatus 300 may receive a signal output from the encodingapparatus of FIG. 2 in the form of a bitstream, and the received signalmay be decoded through the entropy decoder 310. For example, the entropydecoder 310 may parse the bitstream to derive information (e.g.,video/image information) required for image reconstruction (or picturereconstruction). The video/image information may further includeinformation on various parameter sets such as an adaptation parameterset (APS), a picture parameter set (PPS), a sequence parameter set(SPS), a video parameter set (VPS) or the like. Further, the video/imageinformation may further include general constraint information. Thedecoding apparatus may decode a picture further based on information onthe parameter set and/or the general constraint information. In thepresent disclosure, signaled/received information and/or syntaxelements, which will be described later, may be decoded through thedecoding procedure and be obtained from the bitstream. For example, theentropy decoder 310 may decode information in the bitstream based on acoding method such as exponential Golomb encoding, CAVLC, CABAC, or thelike, and may output a value of a syntax element necessary for imagereconstruction and quantized values of a transform coefficient regardinga residual. More specifically, a CABAC entropy decoding method mayreceive a bin corresponding to each syntax element in a bitstream,determine a context model using decoding target syntax elementinformation and decoding information of neighboring and decoding targetblocks, or information of symbol/bin decoded in a previous step, predictbin generation probability according to the determined context model andperform arithmetic decoding of the bin to generate a symbolcorresponding to each syntax element value. Here, the CABAC entropydecoding method may update the context model using information of asymbol/bin decoded for a context model of the next symbol/bin afterdetermination of the context model. Information on prediction amonginformation decoded in the entropy decoder 310 may be provided to thepredictor (inter predictor 332 and intra predictor 331), and residualvalues, that is, quantized transform coefficients, on which entropydecoding has been performed in the entropy decoder 310, and associatedparameter information may be input to the residual processor 320. Theresidual processor 320 may derive a residual signal (residual block,residual samples, residual sample array). Further, information onfiltering among information decoded in the entropy decoder 310 may beprovided to the filter 350. Meanwhile, a receiver (not shown) whichreceives a signal output from the encoding apparatus may furtherconstitute the decoding apparatus 300 as an internal/external element,and the receiver may be a component of the entropy decoder 310.Meanwhile, the decoding apparatus according to the present disclosuremay be called a video/image/picture coding apparatus, and the decodingapparatus may be classified into an information decoder(video/image/picture information decoder) and a sample decoder(video/image/picture sample decoder). The information decoder mayinclude the entropy decoder 310, and the sample decoder may include atleast one of the dequantizer 321, the inverse transformer 322, the adder340, the filter 350, the memory 360, the inter predictor 332, and theintra predictor 331.

The dequantizer 321 may output transform coefficients by dequantizingthe quantized transform coefficients. The dequantizer 321 may rearrangethe quantized transform coefficients in the form of a two-dimensionalblock. In this case, the rearrangement may perform rearrangement basedon an order of coefficient scanning which has been performed in theencoding apparatus. The dequantizer 321 may perform dequantization onthe quantized transform coefficients using quantization parameter (e.g.,quantization step size information), and obtain transform coefficients.

The deqauntizer 322 obtains a residual signal (residual block, residualsample array) by inverse transforming transform coefficients.

The predictor may perform prediction on the current block, and generatea predicted block including prediction samples for the current block.The predictor may determine whether intra prediction or inter predictionis applied to the current block based on the information on predictionoutput from the entropy decoder 310, and specifically may determine anintra/inter prediction mode.

The predictor may generate a prediction signal based on variousprediction methods. For example, the predictor may apply intraprediction or inter prediction for prediction on one block, and, aswell, may apply intra prediction and inter prediction at the same time.This may be called combined inter and intra prediction (CIIP). Inaddition, the predictor may perform intra block copy (IBC) forprediction on a block. The intra block copy may be used for contentimage/video coding of a game or the like, such as screen content coding(SCC). Although the IBC basically performs prediction in a currentblock, it can be performed similarly to inter prediction in that itderives a reference block in a current block. That is, the IBC may useat least one of inter prediction techniques described in the presentdisclosure.

The intra predictor 331 may predict the current block by referring tothe samples in the current picture. The referred samples may be locatedin the neighbor of or apart from the current block according to theprediction mode. In the intra prediction, prediction modes may include aplurality of non-directional modes and a plurality of directional modes.The intra predictor 331 may determine the prediction mode applied to thecurrent block by using the prediction mode applied to the neighboringblock.

The inter predictor 332 may derive a predicted block for the currentblock based on a reference block (reference sample array) specified by amotion vector on a reference picture. At this time, in order to reducethe amount of motion information transmitted in the inter predictionmode, the motion information may be predicted on a block, subblock, orsample basis based on correlation of motion information between theneighboring block and the current block. The motion information mayinclude a motion vector and a reference picture index. The motioninformation may further include inter prediction direction (L0prediction, L1 prediction, Bi prediction, etc.) information. In the caseof inter prediction, the neighboring block may include a spatialneighboring block existing in the current picture and a temporalneighboring block existing in the reference picture. For example, theinter predictor 332 may configure a motion information candidate listbased on neighboring blocks, and derive a motion vector and/or areference picture index of the current block based on received candidateselection information. Inter prediction may be performed based onvarious prediction modes, and the information on prediction may includeinformation indicating a mode of inter prediction for the current block.

The adder 340 may generate a reconstructed signal (reconstructedpicture, reconstructed block, reconstructed sample array) by adding theobtained residual signal to the prediction signal (predicted block,prediction sample array) output from the predictor 330. When there is noresidual for a processing target block as in a case where the skip modeis applied, the predicted block may be used as a reconstructed block.

The adder 340 may be called a reconstructor or a reconstructed blockgenerator. The generated reconstructed signal may be used for intraprediction of a next processing target block in the current block, andas described later, may be output through filtering or be used for interprediction of a next picture.

Meanwhile, in the picture decoding process, luma mapping with chromascaling (LMCS) may be applied.

The filter 350 may improve subjective/objective video quality byapplying the filtering to the reconstructed signal. For example, thefilter 350 may generate a modified reconstructed picture by applyingvarious filtering methods to the reconstructed picture, and may transmitthe modified reconstructed picture in the memory 360, specifically inthe DPB of the memory 360. The various filtering methods may include,for example, deblocking filtering, sample adaptive offset, an adaptiveloop filter, a bilateral filter or the like.

The (modified) reconstructed picture which has been stored in the DPB ofthe memory 360 may be used as a reference picture in the inter predictor332. The memory 360 may store motion information of a block in thecurrent picture, from which motion information has been derived (ordecoded) and/or motion information of blocks in an already reconstructedpicture. The stored motion information may be transmitted to the interpredictor 260 to be utilized as motion information of a neighboringblock or motion information of a temporal neighboring block. The memory360 may store reconstructed samples of reconstructed blocks in thecurrent picture, and transmit them to the intra predictor 331.

In this specification, the examples described in the predictor 330, thedequantizer 321, the inverse transformer 322, and the filter 350 of thedecoding apparatus 300 may be similarly or correspondingly applied tothe predictor 220, the dequantizer 234, the inverse transformer 235, andthe filter 260 of the encoding apparatus 200, respectively.

As described above, prediction is performed in order to increasecompression efficiency in performing video coding. Through this, apredicted block including prediction samples for a current block, whichis a coding target block, may be generated. Here, the predicted blockincludes prediction samples in a space domain (or pixel domain). Thepredicted block may be indentically derived in the encoding apparatusand the decoding apparatus, and the encoding apparatus may increaseimage coding efficiency by signaling to the decoding apparatus notoriginal sample value of an original block itself but information onresidual (residual information) between the original block and thepredicted block. The decoding apparatus may derive a residual blockincluding residual samples based on the residual information, generate areconstructed block including reconstructed samples by adding theresidual block to the predicted block, and generate a reconstructedpicture including reconstructed blocks.

The residual information may be generated through transform andquantization procedures. For example, the encoding apparatus may derivea residual block between the original block and the predicted block,derive transform coefficients by performing a transform procedure onresidual samples (residual sample array) included in the residual block,and derive quantized transform coefficients by performing a quantizationprocedure on the transform coefficients, so that it may signalassociated residual information to the decoding apparatus (through abitstream). Here, the residual information may include valueinformation, position information, a transform technique, transformkernel, a quantization parameter or the like of the quantized transformcoefficients. The decoding apparatus may perform aquantization/dequantization procedure and derive the residual samples(or residual sample block), based on residual information. The decodingapparatus may generate a reconstructed block based on a predicted blockand the residual block. The encoding apparatus may derive a residualblock by dequantizing/inverse transforming quantized transformcoefficients for reference for inter prediction of a next picture, andmay generate a reconstructed picture based on this.

Meanwhile, according to an embodiment, a block differential pulse codedmodulation or Block-based Delta Pulse Code Modulation (BDPCM) techniquemay be used. The BDPCM may also be referred to as a quantized Residualblock-based Delta Pulse Code Modulation (RDPCM).

In the case of predicting a block by applying the BDPCM, reconstructedsamples are utilized to predict a row or a column of a block in a lineby line manner. In this case, a used reference pixel may be unfilteredsamples. A BDPCM direction may represent whether a prediction of avertical direction or horizontal direction is used. A prediction errormay be quantized in a spatial domain, and a pixel may be reconstructedby adding a dequantized prediction error to a prediction. As analternative of the BDPCM, a quantized residual domain BDPCM may beproposed, and a prediction direction or a signaling thereof may be thesame as the BDPCM which has been applied to the spatial domain. In otherwords, quantized coefficients are stacked through a quantized residualdomain BDPCM like in a Delta Pulse Code Modulation (DPCM), and then, aresidual may be reconstructed through dequantization. Accordingly, thequantized residual domain BDPCM may be used in the meaning that the DPCMis applied in a residual coding end. Hereinafter, in the quantizedresidual domain used below, a residual derived based on a prediction isquantized without a transform, and the quantized residual domain means adomain for a quantized residual sample.

For a block of size M (rows)×N (columns), let r_(i,j), 0≤i≤M−1, 0≤j≤N−1be a prediction residual after performing an intra predictionhorizontally (copying left neighbor pixel value across the predictedblock line by line) or vertically (copying top neighbor line to eachline in the predicted block) using unfiltered samples from above or leftblock boundary samples. Further, let Q(r_(i,j)), 0≤i≤M−1, 0≤j≤N−1 denotea quantized version of the residual r_(i,j). Here, the residual means adifference between an original block and a predicted block value.

Thereafter, when the BDPCM is applied to the quantized residual sample,a modified M×N array {tilde over (R)} with elements {tilde over(r)}_(i,j) is derived.

When a vertical BDPCM is signaled, {tilde over (r)}_(i,j) is asrepresented in the Equation below.

$\begin{matrix}{{\overset{\sim}{r}}_{i,j} = \left\{ \begin{matrix}{{{Q\left( r_{i,j} \right)},}\ } & {{i = 0},{0 \leq j \leq \left( {N - 1} \right)}} \\{{{{Q\left( r_{i,j} \right)} - {Q\left( r_{{({i - 1})},j} \right)}},}\ } & {{1 \leq i \leq \left( {M - 1} \right)},\ {0 \leq j \leq \left( {N - 1} \right)}}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{20mu} 1} \right\rbrack\end{matrix}$

For a horizontal prediction, when a similar rule is applied, theresidual quantized sample is as represented in the Equation below.

$\begin{matrix}{{\overset{\sim}{r}}_{i,j} = \left\{ \begin{matrix}{{{Q\left( r_{i,j} \right)},}\ } & {{0 \leq i \leq \left( {M - 1} \right)}\ ,\ {j = 0}} \\{{{{Q\left( r_{i,j} \right)} - {Q\left( r_{i,{({j - 1})}} \right)}},}\ } & {{0 \leq i \leq \left( {M - 1} \right)},\ {1 \leq j \leq \left( {N - 1} \right)}}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{20mu} 2} \right\rbrack\end{matrix}$

The residual quantized sample {tilde over (r)}_(i,j) is transmitted tothe decoding apparatus.

In the decoding apparatus, the above calculations are reversed toproduce Q(r_(i,j)), 0≤i≤M−1, 0≤j≤N−1.

For a vertical prediction, the following equation may be applied.

$\begin{matrix}{{{Q\left( r_{i,j} \right)} = {\sum\limits_{k = 0}^{i}{\overset{\sim}{r}}_{k,j}}},\ {0 \leq i \leq \left( {M - 1} \right)},\ {0 \leq j \leq \left( {N - 1} \right)}} & \left\lbrack {{Equation}\mspace{20mu} 3} \right\rbrack\end{matrix}$

In addition, for a horizontal prediction, the following equation may beapplied.

$\begin{matrix}{{\left( r_{i,j} \right) = {\sum\limits_{k = 0}^{j}{\overset{\sim}{r}}_{i,k}}},\ {0 \leq i \leq \left( {M - 1} \right)}\ ,\ {0 \leq j \leq \left( {N - 1} \right)}} & \left\lbrack {{Equation}\mspace{20mu} 4} \right\rbrack\end{matrix}$

The inverse quantized residual Q⁻¹ (Q(r_(i,j))) is added to the intrablock prediction value to produce the reconstructed sample value.

The main benefit of this scheme is that the inverse BDPCM may beperformed by simply adding the predictor instantaneously in parsing thecoefficient or after parsing during coefficient parsing.

As described above, the BDPCM may be applied to the quantized residualdomain, and the quantized residual domain may include a quantizedresidual (or quantized residual coefficient). In this case, a transformskip may be applied to the residual. That is, for the residual sample, atransform may be skipped, but a quantization may be performed.Alternatively, the quantized residual domain may also include aquantized transform coefficient. A flag on whether the BDPCM isapplicable may be signaled in a sequence level (SPS), and the flag maybe signaled only when it is signaled that the transform skip mode isavailable in SPS.

In applying the BDPCM, an intra prediction for the quantized residualdomain may be performed for the entire block by the sample copy in aprediction direction (e.g., vertical prediction or horizontalprediction) similar to the intra prediction direction. The residual isquantized, and a delta value between the quantized residual and thepredictor for a vertical or horizontal direction (i.e., quantizedresidual in the horizontal or vertical direction), that is, adifferential value {tilde over (r)}_(i,j) is coded.

When a CU is coded in an intra prediction, the flag informationindicating whether the BDPCM is applicable may be transmitted in a CUlevel. That is, the flag information indicates whether the conventionalintra coding is applied or BDPCM is applied. When the BDPCM is applied,a BDPCM prediction direction flag indicating whether a predictiondirection is a horizontal direction or vertical direction may betransmitted. Then, the block is predicted through the conventionalhorizontal or vertical intra prediction procedure using the unfilteredreference sample. The residual is quantized, and a difference valuebetween each quantized residual and the predictor, for example, aquantized residual which is already quantized in a neighboring positionin a horizontal or vertical direction along the BDPCM predictiondirection is coded.

In the case that the BDPCM is applicable, when a CU size is equal to orthe same as MaxTsSize (maximum transform skip size) for a luma sample,and when a CU is coded in an intra prediction, the flag information maybe transmitted in a CU level. Here, MaxTsSize means a maximum block sizefor which the transform skip mode is allowed.

The syntax elements and the semantics therefor for the description aboveare represented in the following table as below.

TABLE 1 Descriptor coding_unit( x0, y0, cbWidth, cbHeight, treeType ) { if( slice_type != I | | sps_ibc_enabled_flag ) {   if( treeType !=DUAL_TREE_CHROMA &&    !( cbWidth = = 4 && cbHeight = = 4 &&!sps_ibc_enabled_flag ) )     cu_skip_flag[ x0 ][ y0 ] ae(v)   if(cu_skip_flag[ x0 ][ y0 ] = = 0 && slice_type != I    && !( cbWidth = = 4&& cbHeight = = 4 ) )     pred_mode_flag ae(v)   if( ( ( slice_type = =I && cu_skip_flag[ x0 ][ y0 ] = =0 ) | |     ( slice_type != I && (CuPredMode[ x0 ][ y0 ] != MODE_INTRA | |     ( cbWidth = = 4 && cbHeight= = 4 && cu_skip_flag[ x0 ][ y0 ] = = 0 ) ) ) ) &&    sps_ibc_enabled_flag && ( cbWidth != 128 | | cbHeight != 128 ) )    pred_mode_ibc_flag ae(v)  }  ...     if( treeType = = SINGLE_TREE || treeType = = DUAL_TREE_LUMA ) {      if( cbWidth <= 32 && cbHeight <=32 )       intra_bdpcm_flag[ x0 ][ y0 ] ae(v)      if( intra_bdpcm_flag[x0 ][ y0 ] )       intra_bdpcm_dir_flag[ x0 ][ y0 ] ae(v) ...

TABLE 2 intra_bdpcm_flag[ x0 ][ y0 ] equal to 1 specifies that BDPCM isapplied to the current luma coding block at the location ( x0, y0 ),i.e. the transform is skipped, the intra luma prediction mode isspecified by intra_bdpcm_dir_flag[ x0 ][ y0 ]. intra_bdpcm_dir_flag[ x0][ y0 ] equal to 0 specifies that BDPCM is not applied to the currentluma coding block at the location ( x0, y0 ). When intra_bdpcm_flag[ x0][ y0 ] is not present it is inferred to be equal to 0. The variableBdpcmFlag[ x ][ y ] is set equal to intra_bdpcm_flag[ x0 ][ y0 ] for x =x0..x0 + cbWidth − 1 and y = y0..y0 + cbHeight − 1.intra_bdpcm_dir_flag[ x0 ][ y0 ] equal to 0 specifies that the BDPCMprediction direction is horizontal. intra_bdpcm_dir_flag[ x0 ][ y0 ]equal to 1 specifies that the BDPCM prediction direction is vertical.The variable BdpcmDir[ x ][ y ] is set equal to intra_bdpcm_dir_flag[ x0][ y0 ] for x = x0..x0 + cbWidth − 1 and y = y0..y0 + cbHeight − 1.

The syntax element “intra_bdpcm_flag” in Table 1 represents whether theBDPCM is applied to a current luma coding block. When the“intra_bdpcm_flag” value is equal to 1, the transform for the codingblock may be skipped, and the prediction mode for the coding block maybe configured to a horizontal or vertical direction by“intra_bdpcm_dir_flag” that represents a prediction direction. When the“intra_bdpcm_flag” does not exist, the value is regarded as zero.

In the case that the “intra_bdpcm_dir_flag” representing a predictiondirection is zero, the case represents that a BDPCM prediction directionis a horizontal direction, and in the case that the“intra_bdpcm_dir_flag” value is 1, the case represents that a BDPCMprediction direction is a vertical direction.

Meanwhile, as described above, an in-loop filtering procedure may beperformed for a reconstructed picture. A modified reconstructed picturemay be generated through the in-loop filtering procedure, and themodified reconstructed picture may be output as a decoded picture in thedecoding apparatus. In addition, the modified reconstructed picture maybe stored in the decoded picture buffer or the memory of the encodingapparatus/decoding apparatus and then, used as a reference picture in aninter prediction procedure in encoding/decoding a picture.

The in-loop filtering procedure may include a deblocking filteringprocedure, a sample adaptive offset (SAO) procedure, and/or an adaptiveloop filter (ALF) procedure. In this case, one or a part of thedeblocking filtering procedure, the sample adaptive offset (SAO)procedure, the adaptive loop filter (ALF) procedure, and a bi-lateralfilter procedure may be sequentially applied, or all of them may besequentially applied. For example, the deblocking filtering proceduremay be applied to a reconstructed picture, and then, the SAO proceduremay be performed. Alternatively, for example, after the deblockingfiltering procedure is applied to a reconstructed picture, the ALFprocedure may be performed. This may be performed in the encodingapparatus in the same manner.

The deblocking filtering is a filtering scheme that removes a distortionoccurred in a boundary between blocks in a reconstructed picture.According to the deblocking filtering procedure, a target boundary isderived in a reconstructed picture, a boundary strength (bS) for thetarget boundary is determined, and the deblocking filtering may beperformed for the target boundary based on the bS. The bS may bedetermined based on prediction modes of two block modes adjacent to thetarget boundary, a motion vector difference, whether a reference pictureis the same, the existence of non-zero valid coefficient, and the like.

The SAO is a method for compensating an offset difference between areconstructed picture and an original picture in a unit of sample andmay be applied based on types such as a Band Offset, an Edge Offset, andthe like. According to the SAO, samples may be classified into differentcategories depending on each SAO type, and an offset value may be addedto each sample based on the category. The filtering information for theSAO may include information on whether the SAO is applied, SAO typeinformation, SAO offset value information, and the like. The SAO mayalso be applied to a reconstructed picture after the deblockingfiltering is applied.

The adaptive loop filter (ALF) is a filtering scheme in a unit of samplebased on filter coefficients according to a filter shape for areconstructed picture. The encoding apparatus may determine whether theALF is applied, an ALF shape, and/or an ALF filtering coefficientthrough a comparison between a reconstructed picture and an originalpicture and signal the result to the decoding apparatus. That is, thefiltering information for the ALF may include information on whether theALF is applied, ALF shape information, ALF filtering coefficientinformation, and the like. The ALF may also be applied to areconstructed picture after the deblocking filtering is applied.

FIG. 4 is a control flowchart for describing a deblocking filteringprocedure according to an embodiment.

Deblocking filtering is applied to a reconstructed picture. Deblockingfiltering is performed for each CU of the reconstructed picture in thesame order of a decoding process. First, a vertical edge is filtered(horizontal filtering), and then, a horizontal edge is filtered(vertical filtering). Deblocking filtering may be applied to edges ofall coding blocks or subblocks and edges of transform blocks of apicture. An output for deblocking filtering may be referred to as amodified reconstructed picture or a modified reconstructed sample/samplearray.

As shown in FIG. 4, the encoding apparatus and the decoding apparatusmay derive a target boundary to be filtered in a reconstructed picture(step S1400).

Thereafter, the encoding apparatus and the decoding apparatus may derivea boundary strength bS (step S1410).

The bS may be determined based on two blocks that face the targetboundary. For example, the bS may be determined based on the followingtable.

TABLE 3  - The variable bS[ xD_(i) ][ yD_(j) ] is derived as follows: - - If cIdx is equal to 0 and both samples p₀ and q₀ are in a codingblock with intra_bdpcm_flag equal to 1, bS[ xD_(i) ][ yD_(j) ] is setequal to 0.  - - Otherwise, if the sample p₀ or q₀ is in the codingblock of a coding unit coded with intra prediction mode, bS[ xD_(i) ][yD_(j) ] is set equal to 2. - Otherwise, if the block edge is also atransform block edge and the sample p₀ or q₀ is in a coding block withciip_flag equal to 1, bS[ xD_(i) ][ yD_(j) ] is set equal to 2. -Otherwise, if the block edge is also a transform block edge and thesample p₀ or q₀ is in a transform block which contains one or morenon-zero transform coefficient levels, bS[ xD_(i) ][ yD_(j) ] is setequal to 1.  - - Otherwise, if the prediction mode of the codingsubblock containing the sample p₀ is different from the prediction modeof the coding subblock containing the sample q₀, bS[ xD_(i) ][ yD_(j) ]is set equal to 1. - Otherwise, if cIdx is equal to 0 and one or more ofthe following conditions are true, bS[ xD_(i) ][ yD_(j) ] is set equalto 1:  - The coding subblock containing the sample p₀ and the codingsubblock containing the sample q₀ are both coded in IBC prediction mode,and the absolute difference between the horizontal or vertical componentof the motion vectors used in the prediction of the two coding subblocksis greater than or equal to 4 in units of quarter luma samples.  - Forthe prediction of the coding subblock containing the sample p₀ differentreference pictures or a different number of motion vectors are used thanfor the prediction of the coding subblock containing the sample q₀.  -One motion vector is used to predict the coding subblock containing thesample p₀ and one motion vector is used to predict the coding subblockcontaining the sample q₀, and the absolute difference between thehorizontal or vertical component of the motion vectors used is greaterthan or equal to 4 in units of quarter luma samples.  - Two motionvectors and two different reference pictures ate used to predict thecoding subblock containing the sample p₀, two motion vectors for thesame two reference pictures are used to predict the coding subblockcontaining the sample q₀ and the absolute difference between thehorizontal or vertical component of the two motion vectors useci in theprediction of the two coding subblocks for the same reference picture isgreater than or equal to 4 in units of quarter luma samples.  - Twomotion vectors for the same reference picture are used to predict thecoding subblock containing the sample p₀, two motion vectors for thesame reference picture are used to predict the coding subblockcontaining the sample q₀ and both of the following conditions are true: - The absolute difference between the horizontal or vertical componentof list 0 motion vectors used in the prediction of the two codingsubblocks is greater than or equal to 4 in quarter luma samples, or theabsolute difference between the horizontal or vertical component of thelist 1 motion vectors used in the prediction of the two coding subblocksis greater than or equal to 4 in units of quarter luma samples. - Theabsolute difference between the horizontal or vertical component of list0 motion vector used in the prediction of the coding subblock containingthe sample p₀ and the list 1 motion vector used in the prediction of thecoding subblock containing the sample q₀ is greater than or equal to 4in units of quarter luma samples, or the absolute difference between thehorizontal or vertical component of the list 1 motion vector used in theprediction of the coding subblock containing the sample p₀ and list 0motion vector used in the prediction of the coding subblock containingthe sample q₀ is greater than or equal to 4 in units of quarter lumasamples. - Otherwise, the variable bS[ xD_(i) ][ yD_(j) ] is set equalto 0.

Here, p and q represent samples of two blocks that face the targetboundary. For example, p₀ may represent a sample of a left or top blockthat faces the target boundary, and q₀ may represent a sample of a rightor bottom block that faces the target boundary. In the case that an edgedirection of the target boundary is vertical, p₀ may represent a sampleof a left block that faces the target boundary, and q₀ may represent asample of a right block that faces the target boundary. In the case thatan edge direction of the target boundary is horizontal, p₀ may representa sample of a top block that faces the target boundary, and q₀ mayrepresent a sample of a bottom block that faces the target boundary.

The encoding apparatus and the decoding apparatus may apply filteringbased on the bS (step S1420).

In the case that the bS value is zero, filtering is not applied to thetarget boundary. Filtering may be performed based on a filteringstrength (strong or weak) and/or a filter length.

Meanwhile, a filter strength according to a reconstructed average lumalevel may be derived as below. FIG. 5 is a diagram illustrating sampleslocated at a boundary of a block.

In HEVC, a filter strength of deblocking filtering may be controlled byvariables β and t_(C) which are derived from an average quantizationparameter qP_(L). In VVC, deblocking filtering may control a strength ofdeblocking filtering by adding an offset to qP_(L) according to a lumalevel of a reconstructed average. The reconstructed luma level LL may bederived as represented in the following equation.

LL=(p _(0,0) +p _(0,3) +q _(0,0) +q _(0,3))>>2)/(1<<bitDepth)  [Equation5]

Here, a position of sample values p_(i,k) and q_(i,k) in which i is 0 to3, and k is 0 to 3 may be identified in FIG. 5.

The variable qP_(L) may be derived as represented in the followingequation.

qP _(L)=((Qp _(Q) +Qp _(P)+1)>>1)+qpOffset

Here, Q_(p) _(Q) and Q_(p) _(P) represent quantization parametersincluding samples q_(0,0) and p_(0,0), respectively, and the offsetvalue qpOffset that depends on a transform procedure may be signaled ina sequence parameter set (SPS).

Meanwhile, stronger filtering may be applied to a luma sample. In thecase that a sample located at one side boundary belongs to a largeblock, a duplicated linear filter (stronger deblocking filter) may beapplied. The sample that belongs to the large block may be defined as asample that belongs to each boundary in the case that a width is equalto or greater than 32 for a vertical boundary or a height is equal to orgreater than 32 for a horizontal boundary.

Meanwhile, strong filtering for a chroma sample may be performed asrepresented in the following equation.

p ₂′=(3*p ₃+2*p ₂ +p ₁ +p ₀ +q ₀+4)>>3

p ₁′=(2*p ₃ +p ₂+2*p ₁ +p ₀ +q ₀ +q ₁+4)>>3

p ₀′=(p3÷p2+p1+2*p0+q0+q1+q2+4)>>3  [Equation 7]

Chroma filtering represented in Equation 7 is performed on an 8×8 chromasample grid. Strong filtering for a chroma sample may be performed inboth sides of a block boundary. Here, chroma filtering may be selectedin the case that both edges of the chroma sample are equal to or greaterthan 8 in a unit of chroma sample and performed in the case that adetermination for the following three conditions is satisfied. First, adetermination for a boundary strength (bS) and a large block, and thesecond and third determinations are a determination for filtering on/offand a determination for the strong filter, respectively, which are thesame as the determinations for HEVC luma block, basically. An example ofdetermining a boundary strength (bS) for a chroma block is asrepresented in the following table.

TABLE 4 Conditions Y (luma) U (chroma) V (chroma) At least one of theadjacent 2 2 2 blocks is intra At least one of the adjacent 1 1 1 blockshas non-zero transform coefficients Absolute difference between 1 N/AN/A the motion vectors that belong to the adjacent blocks is greaterthan or equal to one integer luma sample Motion prediction in the 1 N/AN/A adjacent blocks relets to vectors is different Otherwise 0 0 0

As represented in Table 4, deblocking for a chroma sample may beperforming when the bS is equal to 2, or the bS is equal to 1 when alarge block boundary is detected. The second and third conditions arebasically the same as the strong filtering determination applied to anHEVC luma sample.

In VVC, deblocking filter may be applied for a subblock boundary, andaccording to an example, deblocking filter may be performed on an 8×8grid. The deblocking filtering process may be applied to a CU boundaryas well as the subblock boundary, which are aligned with an 8×8 grid.

The subblock boundary may include the prediction unit (PU) boundaryintroduced by a subblock-based temporal motion vector prediction (STMVP)and an affine mode, and the transform unit (TU) boundary introduced by asubblock transform (SBT) and an ISP (intra subpartitions) mode.

For a subblock on an 8×8 grid to which the SBT or the ISP are applied,the same procedure as the procedure applied in a TU deblocking filter ofHEVC is applied. Deblocking filtering is applied to a TU boundary on an8×8 grid when there are non-zero coefficients in either one of subblockacross an edge.

For a subblock on an 8×8 grid to which the STMVP and affine modes areapplied, the same procedure as the procedure applied in a TU deblockingfilter of HEVC is applied. Deblocking filtering is applied to a PUboundary on an 8×8 grid with the consideration of the difference betweenmotion vectors and reference pictures of a neighboring subblock.

Hereinafter, among the in-loop filtering process for a block to whichthe BDPCM is applied, a deblocking filtering method may be proposed. Inan example, in the process of encoding and decoding an image or a video,in the case that a luma block is coded in the BDPCM a single tree type,a boundary strength (bS) of a corresponding chroma block may be set asthe same as the luma block. That is, in the case that a tree type is thesingle tree, in order to determine whether deblocking filtering isapplied to a block coded in the BDPCM, when the bS is calculated, the bSfor the chroma block may be determined as below.

FIG. 6 is a diagram illustrating a method for determining a bS accordingto an embodiment of the present disclosure.

According to an example, in the case that two blocks are BDPCM codedbased on an edge, a bS may be derived as zero. That is, for a chromablock, without regard to whether the BDPCM is applied, in the case thata corresponding luma block is BDPCM coded, the bS of the chroma blockmay be derived as zero in the single tree type.

In FIG. 6, the large block in the left side may represent a luma block,and the small blocks in the right side may represent chroma blocksaccording to components (Cb and Cr).

As shown in FIG. 6, the bS in a block boundary may be determinedaccording to a coding scheme of two neighboring luma blocks, and the bSof the chroma block may be set as the same as the bS of the luma block.

The two neighboring luma blocks shown in the top side may be codedaccording to the BDPCM and the inter prediction, respectively, and inthis case, the bS may be set to 1 or 0. In addition, the two neighboringluma blocks shown in the bottom side may be coded according to the BDPCMand the intra prediction, respectively, and in this case, the bS mayalso be set to 1 or 0. In both two cases, the bS of the chroma block maybe set as the same as the bS of the luma block.

In addition, in the case that both two neighboring luma blocks are codedin the BDPCM like the luma blocks shown in the middle, the bS for aboundary of the two blocks may be set to zero, and in this case, for thechroma block corresponding to the luma block, the bS for deblockingfiltering may also be set to zero.

Whether the luma block is coded in the BDPCM scheme may be signaled withflag information such as intra_bdpcm_flag represented in Table 1.

As such, in the case that the bS is set to zero, deblocking filtering isnot performed. That is, in the case that both two neighboring lumablocks are coded in the BDPCM scheme according to an embodiment, the bSsof the luma block and the chroma block are set to zero, and deblockingfiltering is not performed.

Such a bS determination method is as represented in the following table.

TABLE 5 1.1.1.1 Derivation process of boundary filtering strength Inputsto this process are:  -  a picture sample array recPicture,  -  alocation ( xCb, yCb ) specifying the top-left sample of the currentcoding block  relative to the top left sample of the current picture,  - a variable nCbW specifying the width of the current coding block,  -  avariable nCbH specifying the height of the current coding block,  -  avariable edgeType specifying whether a vertical (EDGE_VER) or ahorizontal  (EDGE_HOR) edge is filtered,  -  a variable cIdx specifyingthe colour component of the current coding block,  -  a two-dimensional(nCbW)×(nCbH) array edgeFlags. Output of this process is atwo-dimensional (nCbW)×(nCbH) array bS specifying the boundary filtering strength. The variables xD_(i), yD_(j), xN and yN are derivedas follows:  -  If edgeType is equal to EDGE_VER, xD_(i) = ( i << 3 )(8-1026) yD_(j) = cIdx = = 0 ? ( j << 2 ) : ( j << 1 ) (8-1027) xN isset equal to Max( 0, ( nCbW / 8 ) − 1 ) (8-1028) yN = cIdx = = 0 ? (nCbH / 4 ) − 1 : ( nCbH / 2 ) − 1 (8-1029)  -  Otherwise (edgeType isequal to EDGE_HOR), xD_(i) = cIdx = = 0 ? ( i << 2 ) : ( i << 1 )(8-1030) yD_(j) = ( j << 3 ) (8-1031) xN = cIdx = = 0 ? ( nCbW / 4 ) − 1: ( nCbW / 2 ) − 1 (8-1032) yN = Max( 0, ( nCbH / 8 ) − 1 ) (8-1033) ForxD_(i) with i = 0..xN and yD_(j) with j = 0..yN, the following applies: -  If edgeFlags[ xD_(i) ][ yD_(j) ] is equal to 0, the variable bS[xD_(i) ][ yD_(j) ] is set equal to 0.  -  Otherwise, the followingapplies:  - The sample values p₀ and q₀ are derived as follows: - IfedgeType is equal to EDGE_VER, p₀ is set equal to recPicture[ xCb +xD_(i) − 1 ][ yCb + yD_(j) ] and q₀ is set equal to recPicture[ xCb +xD_(i) ][ yCb + yD_(j) ]. - Otherwise (edgeType is equal to EDGE_HOR),p₀ is set equal to recPicture[ xCb + xD_(i) ][ yCb + yD_(j) − 1 ] and q₀is set equal to recPicture[ xCb + xD_(i) ][ yCb + yD_(j) ].  - Thevariable bS[ xD_(i) ][ yD_(j) ] is derived as follows: - If both samplesp₀ and q₀ are in a coding block with intra_bdpcm_flag equal to 1, bS[xD_(i) ][ yD_(j) ] is set equal to 0. - Otherwise, if the sample p₀ orq₀ is in the coding block of a coding unit coded with intra predictionmode, bS[ xD_(i) ][ yD_(j) ] is set equal to 2. - Otherwise, if theblock edge is also a transform block edge and the sample p₀ or q₀ is ina coding block with ciip_flag equal to 1, bS[ xD_(i) ][ yD_(j) ] is setequal to 2.  - Otherwise, if the block edge is also a transform blockedge and the sample p₀ or q₀ is in a transform block which contains oneor more non-zero transform coefficient levels, bS[ xD_(i) ][ yD_(j) ] isset equal to 1.  - Otherwise, if the prediction mode of the codingsubblock containing the sample p₀ is different from the prediction modeof the coding subblock containing the sample q₀, bS[ xD_(i) ][ yD_(j) ]is set equal to 1.  - Otherwise, if cIdx is equal to 0 and one or moreof the following conditions are true, bS[ xD_(i) ][ yD_(j) ] is setequal to 1:  - The coding subblock containing the sample p₀ and thecoding subblock containing the sample q₀ are both coded in IBCprediction mode, and the absolute difference between the horizontal orvertical component of the motion vectors used in the prediction of thetwo coding subblocks is greater than or equal to 4 in units of quarterluma samples.  - For the prediction of the coding subblock containingthe sample p₀ different reference pictures or a different number ofmotion vectors are used than for the prediction of the coding subblockcontaining the sample q₀.  - One motion vector is used to predict thecoding subblock containing the sample p₀ and one motion vector is usedto predict the coding subblock containing the sample q₀, and theabsolute difference between the horizontal or vertical component of themotion vectors used is greater than or equal to 4 in units of quarterluma samples.  - Two motion vectors and two different reference picturesare used to predict the coding subblock containing the sample p₀, twomotion vectors for the same two reference pictures are used to predictthe coding subblock containing the sample q₀ and the absolute differencebetween the horizontal or vertical component of the two motion vectorsused in the prediction of the two coding subblocks for the samereference picture is greater than or equal to 4 in units of quarter lumasamples.  - Two motion vectors for the same reference picture are usedto predict the coding subblock containing the sample p₀, two motionvectors for the same reference picture are used to predict the codingsubblock containing the sample q₀ and both of the following conditionsare true:  - The absolute difference between the horizontal or verticalcomponent of list 0 motion vectors used in the prediction of the twocoding subblocks is greater than or equal to 4 in quarter luma samples,or the absolute difference between the horizontal or vertical componentof the list 1 motion vectors used in the prediction of the two codingsubblocks is greater than or equal to 4 in units of quarter lumasamples.  - The absolute difference between the horizontal or verticalcomponent of list 0 motion vector used in the prediction of the codingsubblock containing the sample p₀ and the list 1 motion vector used inthe prediction of the coding subblock containing the sample q₀ isgreater than or equal to 4 in units of quarter luma samples, or theabsolute difference between the horizontal or vertical component of thelist 1 motion vector used in the prediction of the coding subblockcontaining the sample p₀ and list 0 motion vector used in the predictionof the coding subblock containing the sample q₀ is greater than or equalto 4 in units of quarter luma samples. - Otherwise, the variable bS[xD_(i) ][ yD_(j) ] is set equal to 0. NOTE 1 - The determination ofwhether the reference pictures used for the two coding sublocks are thesame or different is based only on which pictures are referenced,without regard to whether a prediction is formed using an index intoreference picture list 0 or an index into reference picture list 1, andalso without regard to whether the index position within a referencepicture list is different. NOTE 2 - The number of motion vectors thatare used for the prediction of a coding subblock with top-left samplecovering ( xSb, ySb ), is equal to PredFlagL0[ xSb ][ ySb ] +PredFlagL1[ xSb ][ ySb ].

In Table 5, as described above, in the case that a target boundary is avertical boundary, based on the target boundary, a left block may beindicated as P, and a right block may be indicated as Q. Further, in thecase that a target boundary is a horizontal boundary, based on thetarget boundary, a top block may be indicated as P, and a bottom blockmay be indicated as Q.

The variable bS[xDi][yDj] for the bS may be derived as one of 0, 1, and2.

As represented in Table 5, in the case that both samples p₀ and q₀ arein a coding block with intra_bdpcm_flag equal to 1, bS[xDi][yDj] is setequal to 0. In this case, deblocking filtering is not performed.

Otherwise, in the case that the sample p₀ or q₀ is in the coding blockof a coding unit coded with the intra prediction mode, bS[xDi][yDj] isset equal to 2.

In addition, in the case that the block edge is also a transform blockedge and the sample p₀ or q₀ is in a transform block which contains oneor more non-zero transform coefficient levels, bS[xDi][yDj] is set equalto 1.

Alternatively, in the case that two blocks are coded with differentprediction modes or different reference picture or different number ofmotion vectors are used, bS[xDi][yDj] may be set equal to 1.

Meanwhile, according to another example, bdpcm flag information may besignaled as represented in the following table.

TABLE 6 7.3.2.3 Sequence parameter set RBSP syntax sps_sao_enabled_flagu(1) sps_alf_enabled_flag u(1) if( sps_alf_enabled_flag &&ChromaArrayType != 0 )  sps_ccalf_enabled_flag u(1)sps_transform_skip_enabled_flag u(1) if( sps_transform_skip_enabled_flag) {  log2_transform_skip_max_size_minus2 ue(v)  sps_bdpcm_enabled_flagu(1) 7.4.3.3 Sequence parameter set RBSP semanticssps_bdpcm_enabled_flag equal to 1 specifies that intra_bdpcm_luma_flagand intra_bdpcm_chroma_flag may be present in the coding unit syntax forintra coding units. sps_bdpcm_enabled_flag equal to 0 specifies thatintra_bdpcm_luma_flag and intra_bdpcm_chroma_flag are not present in thecoding unit syntax for intra coding units. When not present, the valueof sps_bdpcm_enabled_flag is inferred to be equal to 0.

Table 6 represents “sps_bdpcm_enabled_flag” signaled in a sequenceparameter set (SPS). In the case that the syntax element“sps_bdpcm_enabled_flag” is 1, the case represents that the flaginformation representing whether the BDPCM is applied to a coding unitfor which the intra prediction is performed, that is,intra_bdpcm_luma_flag” and “intra_bdpcm_chroma_flag” are present in thecoding unit.

In the case that the syntax element “sps_bdpcm_enabled_flag” is notpresent, the value is regarded as zero.

TABLE 7  7.3.10.5 Coding unit syntax   if( sps_bdpcm_enabled_flag &&    cbWidth <= MaxTsSize && cbHeight <= MaxTsSize )   intra_bdpcm_luma_flag ae(v)   if( intra_bdpcm_luma_flag )   intra_bdpcm_luma_dir_flag ae(v) if( ( treeType = = SINGLE_TREE | |treeType = = DUAL_TREE_CHROMA ) &&   ChromaArrayType != 0 ) {  if(pred_mode_plt_flag && treeType = = DUAL_TREE_CHROMA )   palette_coding(x0, y0, cbWidth / SubWidthC, cdHeight / SubHeightC, treeType )  else if(!pred_mode_plt_flag ) {   if( !cu_act_enabled_flag ) {    if( cbWidth /SubWidthC <= MaxTsSize && cbHeight / SubHeightC <= MaxTsSize      &&sps_bdpcm_enabled_flag )     intra_bdpcm_chroma_flag ae(v)    if(intra_bdpcm_chroma_flag )     intra_bdpcm_chroma_dir_flag ae(v) 7.4.11.5Coding unit semantics intra_bdpcm_luma_flag equal to 1 specifies thatBDPCM is applied to the current luma coding block at the location ( x0,y0 ), i.e. the transform is skipped, the intra luma prediction mode isspecified by intra_bdpcm_luma_dir_flag. intra_bdpcm_luma_flag equal to 0specifies that BDPCM is not applied to the current luma coding block atthe location ( x0, y0 ), When intra_bdpcm_luma_flag is not present it isinferred to be equal to 0. The variable BdpcmFlag[ x ][ y ][ cIdx ] isset equal to intra_bdpcm_luma_flag for x = x0..x0 + cbWidth − 1, y =y0..y0 + cbHeight − 1 and cIdx = 0. intra_bdpcm_luma_dir_flag equal to 0specifies that the BDPCM prediction direction is horizontal.intra_bdpcm_luma_dir_flag equal to 1 specifies that the BDPCM predictiondirection is vertical. The variable BdpcmDir[ x ][ y ][ cIdx ] is setequal to intra_bdpcm_luma_dir_flag for x = x0..x0 + cbWidth − 1, y =y0..y0 + cbHeight − 1 and cIdx = 0. intra_bdpcm_chroma_flag equal to 1specifies that BDPCM is applied to the current chroma coding blocks atthe location ( x0, y0 ), i.e. the transform is skipped, the intra chromaprediction mode is specified by intra_bdpcm_chroma_dir_flag.intra_bdpcm_chroma_flag equal to 0 specifies that BDPCM is not appliedto the current chroma coding blocks at the location ( x0, y0 ). Whenintra_bdpcm_chroma_flag is not present it is inferred to be equal to 0.The variable BdpcmFlag[ x ][ y ][ cIdx ] is set equal tointra_bdpcm_chroma_flag for x = x0..x0 + cbWidth − 1, y = y0..y0 +cbHeight − 1 and cIdx = 1..2. intra_bdpcm_chroma_dir_flag equal to 0specifies that the BDPCM prediction direction is horizontal.intra_bdpcm_chroma_dir_flag equal to 1 specifies that the BDPCMprediction direction is vertical. The variable BdpcmDir[ x ][ y ][ cIdx] is set equal to intra_dbpcm_chroma_dir_flag for x = x0..x0 + cbWidth −1, y = y0..y0 + cbHeight − 1 and cIdx = 1..2.

The syntax element “intra_bdpcm_lumaflag” and “intra_bdpcm_chroma_flag”represented in Table 6 represents whether the BDPCM is applied to acurrent luma coding block or a current chroma coding block. In the casethat “intra_bdpcm_luma_flag” or “intra_bdpcm_chroma_flag” is 1, thetransform for the coding block may be skipped, and a prediction mode forthe coding block may be set in a horizontal or vertical direction by“intra_bdpcm_lumadir_flag” or “intra_bdpcm_chromadirflag” thatrepresents a prediction direction. In the case that“intra_bdpcm_luma_flag” or “intra_bdpcm_chroma_flag” is not present, thevalue is regarded as zero.

“intra_bdpcm_chroma_flag” may be signaled for a chroma coding block ofwhich a current block is a single tree type or a dual tree chroma.

In the case that “intra_bdpcm_lumadirflag” or“intra_bdpcm_chromadirflag” that represents a prediction direction iszero, the case represents that a BDPCM prediction direction is ahorizontal direction, and in the case that “intra_bdpcm_luma_dir_flag”or “intra_bdpcm_chroma_dir_flag” value is 1, the case represents that aBDPCM prediction direction is a vertical direction.

A bS determination method according to the flag information representedin Table 6 and Table 7 is represented as below.

TABLE 8 For xD, with i = 0..xN and yD_(i) with j = 0..yN, the followingapplies:  - If edgeFlags[ xD_(i) ][ yD_(j) ] is equal to 0, the variablebS[ xD_(i) ][ yD_(j) ] is set equal to 0.  - Otherwise, if edgeType isequal to EDGE_VER, VirtualBoundariesPresentFlag equal to 1, and ( xCb +xD_(i) ) is equal to VirtualBoundariesPosX[ n ] for any n =0..NumVerVirtualBoundaries − 1, the variable bS[ xD_(i) ][ yD_(j) ] isset equal to 0.  - Otherwise, if edgeType is equal to EDGE_HOR,VirtualBoundariesPresentFlag equal to 1, and ( yCb + yD_(j) ) is equalto VirtualBoundariesPosY[ n ] for any n = 0..NumHorVirtualBoundaries −1, the variable bS[ xD_(i) ][ yD_(j) ] is set equal to 0.  - Otherwise,the following applies: - The sample values p₀ and q₀ are derived asfollows: - If edgeType is equal to EDGE_VER, p₀ is set equal torecPicture[ xCb + xD_(i) − 1 ][ yCb + yD_(j) ] and q₀ is set equal torecPicture[ xCb + xD_(i) ][ yCb + yD_(j) ]. - Otherwise (edgeType isequal to EDGE_HOR), p₀ is set equal to recPicture[ xCb + xD_(i) ][ yCb +yD_(j) − 1 ] and q₀ is set equal to recPicture[ xCb + xD_(i) ][ yCb +yD_(j) ]. - The variable bS[ xD_(i) ][ yD_(j) ] is derived as follows: -If cIdx is equal to 0 and both samples p₀ and q₀ are in a coding blockwith intra_bdpcm_luma_flag equal to 1, bS[ xD_(i) ][ yD_(j) ] is setequal to 0. - Otherwise, if cIdx is greater than 0 and both samples p₀and q₀ are in a coding block with intra_bdpcm_chroma_flag equal to 1,bS[ xD_(i) ][ yD_(j) ] is set equal to 0. - Otherwise, if the sampke p₀or q₀ is in the coding block of a coding unit coded with CuPredModeequal to MODE_INTRA, bS[ xD_(i) ][ yD_(j) ] is set equal to 2. -Otherwise, if the block edge is also a coding block edge and the samplep₀ or q₀ is in a coding block with ciip_flag equal to 1, bS[ xD_(i) ][yD_(j) ] is set equal to 2.

As represented in Table 8, according to an example, whether twoneighboring luma blocks are coded in the BDPCM may be indicated byintra_bdpcm_luma_flag. In the case that intra_bdpcm_luma_flag value is1, bS[xDi][yDj] for a luma block may be set to zero.

In addition, whether two neighboring chroma blocks are coded in theBDPCM may be indicated by intra_bdpcm_chroma_flag. In the case thatintra_bdpcm_chroma_flag is 1, bS[xDi][yDj] for a luma block may be setto zero.

That is, the flag information for the BDPCM may be signaled for each ofthe luma block and the chroma block, and in the case that the flag valueis 1, the bS for deblocking filtering may be set to zero. That is, forthe block coded in the BDPCM scheme, deblocking filtering may not beperformed.

The following drawings are provided to describe specific examples of thepresent disclosure. Since the specific designations of devices or thedesignations of specific signals/messages/fields illustrated in thedrawings are provided for illustration, technical features of thepresent disclosure are not limited to specific designations used in thefollowing drawings.

FIG. 7 is a control flowchart for describing a video decoding methodaccording to an embodiment of the present disclosure.

The decoding apparatus 300 receives coding information such as BDPCMinformation from a bitstream (step S710).

The BDPCM information may include BDPCM flag information that indicateswhether the BDPCM is applied to a current block and directionalinformation for a direction in which the BDPCM is performed.

When the BDPCM is applied to the current block, the BDPCM flag value maybe 1, and when the BDPCM is not applied to the current block, the BDPCMflag value may be zero.

Meanwhile, a tree type of the current block may be classified into asingle tree SINGLE_TREE or a dual tree DUAL_TREE according to whether achroma block corresponding to a luma block has an individual partitionstructure. In the case that a chroma block has the same partitionstructure as a luma block, the case may represent the single tree, andin the case that a chroma component block has a different partitionstructure from a luma component block, the case may represent the dualtree. According to an example, the BDPCM may be individually applied toa luma block or a chroma block of the current block. When the BDPCM isapplied to a luma block, a transform index for the luma block may not bereceived, and when the BDPCM is applied to a chroma block, a transformindex for the chroma block may not be received.

In the case that a tree structure of the current block is the dual tree,the BDPCM may be applied to only one component block, and even in thecase that the current block is the single tree structure, the BDPCM maybe applied to only one component block.

Meanwhile, the directional information for the BDPCM may indicate ahorizontal direction or a vertical direction. According to thedirectional information, quantization information may be derived, and aprediction sample may be derived.

The decoding apparatus 300 may derive a quantized transform coefficientfor the current block, that is, untransformed quantized residual samplesbased on the BDPCM and derive a residual sample by performingdequantization for the quantized residual samples (step S720).

In the case the BDPCM is applied to the current block, the residualinformation received in the decoding apparatus 300 may a differentialvalue of the quantized residuals. According to a BDPCM direction, adifferential value of quantized residuals of a line of a previousvertical or horizontal direction and a specific line may be received,and the decoding apparatus 300 may add the quantized residuals of a lineof a previous vertical or horizontal direction to the receiveddifferential value of quantized residuals and derive a quantizedresidual of a specific line. The quantized residual may be derived basedon Equation 3 or Equation 4.

As described above, when the BDPCM is applied to the current block, adequantized transform coefficient may be derived as a residual samplewithout going through a transform procedure.

The intra predictor 331 may perform an intra prediction for the currentblock based on the BDPCM information, that is, the directionalinformation in which the BDPCM is performed and derive predictionsamples (step S730).

When the BDPCM is applied to the current block, an intra prediction maybe performed using the BDPCM, and this may mean that the BDPCM may beapplied only to an intra slice or intra coding block predicted in theintra mode.

The intra prediction may be performed based on the directionalinformation for the BDPCM, and the intra prediction mode of the currentblock may be either one of a horizontal directional mode or a verticaldirectional mode.

The decoding apparatus 300 may generate a reconstructed picture based onthe derived residual sample and the prediction sample (step S740).

The decoding apparatus 300 may perform deblocking filtering, which isone of in-loop filtering methods based on the BDPCM information, for thereconstructed picture (step S750). In this case, when BDPCM flaginformation is 1, the boundary strength (bS) is derived as zero, anddeblocking filtering may not be performed.

According to an example, in the case that a luma block is coded in theBDPCM in the single tree type, the boundary strength (bS) of acorresponding chroma block may be set as the same as the luma block.

In the case that two blocks are BDPCM coded based on an edge betweenblocks, the bS may be derived as zero. That is, for a chroma block,without regard to whether the BDPCM is applied, in the case that acorresponding luma block is BDPCM coded, the bS of the chroma block maybe derived as zero in the single tree type.

As such, in the case that the bS is set to zero, deblocking filtering isnot performed. That is, in the case that both two neighboring lumablocks are coded in the BDPCM scheme according to an embodiment, the bSsof the luma block and the chroma block are set to zero, and deblockingfiltering is not performed.

Alternatively, according to another example, whether two neighboringluma blocks are coded in the BDPCM may be indicated byintra_bdpcm_luma_flag. In the case that intra_bdpcm_luma_flag value is1, bS[xDi][yDj] for a luma block may be set to zero. In addition,whether two neighboring chroma blocks are coded in the BDPCM may beindicated by intra_bdpcm_chroma_flag. In the case thatintra_bdpcm_chroma_flag is 1, bS [xDi][yDj] for a luma block may be setto zero.

That is, the flag information for the BDPCM may be signaled for each ofthe luma block and the chroma block, and in the case that the flag valueis 1, the bS for deblocking filtering may be set to zero. That is, forthe block coded in the BDPCM scheme, deblocking filtering may not beperformed.

In summary, the BDPCM information received in the decoding apparatus mayinclude flag information indicating whether the BDPCM is applied to thecurrent block, and when the flag information is 1, the boundary strength(bS) for deblocking filtering may be derived as zero.

In this case, the current block may be either one of a luma coding blockor a chroma coding block, and in the case that a tree type of thecurrent block is the single tree type and a chroma coding block, whenthe flag information is 1, the boundary strength may be derived as 1.

The following drawings are provided to describe specific examples of thepresent disclosure. Since the specific designations of devices or thedesignations of specific signals/messages/fields illustrated in thedrawings are provided for illustration, technical features of thepresent disclosure are not limited to specific designations used in thefollowing drawings.

FIG. 8 is a control flowchart for describing a video encoding methodaccording to an embodiment of the present disclosure.

The encoding apparatus 200 may derive prediction samples for a currentblock based on the BDPCM (step S810).

The encoding apparatus 200 may derive an intra prediction sample for thecurrent block based on a specific direction in which the BDPCM isperformed. The specific direction may be a vertical direction or ahorizontal direction, and according to the intra prediction mode, aprediction sample for the current block may be generated.

Meanwhile, a tree type of the current block may be classified into asingle tree SINGLE_TREE or a dual tree DUAL_TREE according to whether achroma block corresponding to a luma block has an individual partitionstructure. In the case that a chroma block has the same partitionstructure as a luma block, the case may represent the single tree, andin the case that a chroma component block has a different partitionstructure from a luma component block, the case may represent the dualtree. According to an example, the BDPCM may be individually applied toa luma block or a chroma block of the current block.

In the case that a tree structure of the current block is the dual tree,the BDPCM may be applied to only one component block, and even in thecase that the current block is the single tree structure, the BDPCM maybe applied to only one component block.

Alternatively, according to an example, the BDPCM may be applied only inthe case that a width of the current block is a first threshold value orsmaller and a height of the current block is a second threshold value orsmaller. The first threshold value and the second threshold value may be32 and set to a maximum height or a maximum width of a transform blockin which transform is performed.

The encoding apparatus 200 may derive residual samples for the currentblock based on a prediction block (step S820) and generate areconstructed picture based on the residual sample and the predictionsample (step S830).

The encoding apparatus 200 may perform deblocking filtering, which isone of in-loop filtering methods based on the BDPCM information, for thereconstructed picture (step S840). In this case, when BDPCM flaginformation is 1, the boundary strength (bS) is derived as zero, anddeblocking filtering may not be performed.

According to an example, in the case that a luma block is coded in theBDPCM in the single tree type, the boundary strength (bS) of acorresponding chroma block may be set as the same as the luma block.

In the case that two blocks are BDPCM coded based on an edge betweenblocks, the bS may be derived as zero. That is, for a chroma block,without regard to whether the BDPCM is applied, in the case that acorresponding luma block is BDPCM coded, the bS of the chroma block maybe derived as zero in the single tree type.

As such, in the case that the bS is set to zero, deblocking filtering isnot performed. That is, in the case that both two neighboring lumablocks are coded in the BDPCM scheme according to an embodiment, the bSsof the luma block and the chroma block are set to zero, and deblockingfiltering is not performed.

Alternatively, according to another example, according to whether twoluma blocks are coded in the BDPCM, bS[xDi][yDj] for a luma block may bederived as zero, and according to whether two chroma blocks are coded inthe BDPCM, bS[xDi][yDj] for a chroma block may be derived as zero.

In addition, the flag information for the BDPCM may be coded for each ofthe luma block and the chroma block, and in the case that the flag valueis 1, the bS for deblocking filtering may be set to zero. That is, forthe block coded in the BDPCM scheme, deblocking filtering may not beperformed.

Thereafter, the encoding apparatus 200 may derive quantized residualinformation based on the BDPCM.

The encoding apparatus 200 may derive a quantized residual sample of aspecific line and a differential value of a quantized residual sample ofa line of a previous vertical or horizontal direction and a specificline as the quantized residual information. That is, a differentialvalue of a quantized residual, not the conventional residual, isgenerated as the residual information, which may be derived based onEquation 1 or Equation 2.

The encoding apparatus 200 may encode the quantized residual informationand coding information for the current block, for example, the BDPCMinformation for the BDPCM (step S850).

The BDPCM information may include BDPCM flag information that indicateswhether the BDPCM is applied to a current block and directionalinformation for a direction in which the BDPCM is performed.

When the BDPCM is applied to the current block, the BDPCM flag value maybe encoded to 1, and when the BDPCM is not applied to the current block,the BDPCM flag value may be encoded to zero.

In addition, as described above, in the case that a tree structure ofthe current block is the dual tree, the BDPCM may be applied to only onecomponent block, and even in the case that the current block is thesingle tree structure, the BDPCM may be applied to only one componentblock.

The directional information for the BDPCM may indicate a horizontaldirection or a vertical direction.

In the present disclosure, at least one of quantization/dequantizationand/or transform/inverse transform may be omitted. Whenquantization/dequantization is omitted, a quantized transformcoefficient may be referred to as a transform coefficient. Whentransform/inverse transform is omitted, the transform coefficient may bereferred to as a coefficient or a residual coefficient, or may still bereferred to as a transform coefficient for consistency of expression.

In addition, in the present disclosure, a quantized transformcoefficient and a transform coefficient may be referred to as atransform coefficient and a scaled transform coefficient, respectively.In this case, residual information may include information on atransform coefficient(s), and the information on the transformcoefficient(s) may be signaled through a residual coding syntax.Transform coefficients may be derived based on the residual information(or information on the transform coefficient(s)), and scaled transformcoefficients may be derived through inverse transform (scaling) of thetransform coefficients. Residual samples may be derived based on theinverse transform (transform) of the scaled transform coefficients.These details may also be applied/expressed in other parts of thepresent disclosure.

In the above-described embodiments, the methods are explained on thebasis of flowcharts by means of a series of steps or blocks, but thepresent disclosure is not limited to the order of steps, and a certainstep may be performed in order or step different from that describedabove, or concurrently with another step. Further, it may be understoodby a person having ordinary skill in the art that the steps shown in aflowchart are not exclusive, and that another step may be incorporatedor one or more steps of the flowchart may be removed without affectingthe scope of the present disclosure.

The above-described methods according to the present disclosure may beimplemented as a software form, and an encoding apparatus and/ordecoding apparatus according to the disclosure may be included in adevice for image processing, such as, a TV, a computer, a smartphone, aset-top box, a display device or the like.

When embodiments in the present disclosure are embodied by software, theabove-described methods may be embodied as modules (processes, functionsor the like) to perform the above-described functions. The modules maybe stored in a memory and may be executed by a processor. The memory maybe inside or outside the processor and may be connected to the processorin various well-known manners. The processor may include anapplication-specific integrated circuit (ASIC), other chipset, logiccircuit, and/or a data processing device. The memory may include aread-only memory (ROM), a random access memory (RAM), a flash memory, amemory card, a storage medium, and/or other storage device. That is,embodiments described in the present disclosure may be embodied andperformed on a processor, a microprocessor, a controller or a chip. Forexample, function units shown in each drawing may be embodied andperformed on a computer, a processor, a microprocessor, a controller ora chip.

Further, the decoding apparatus and the encoding apparatus to which thepresent disclosure is applied, may be included in a multimediabroadcasting transceiver, a mobile communication terminal, a home cinemavideo device, a digital cinema video device, a surveillance camera, avideo chat device, a real time communication device such as videocommunication, a mobile streaming device, a storage medium, a camcorder,a video on demand (VoD) service providing device, an over the top (OTT)video device, an Internet streaming service providing device, athree-dimensional (3D) video device, a video telephony video device, anda medical video device, and may be used to process a video signal or adata signal. For example, the over the top (OTT) video device mayinclude a game console, a Blu-ray player, an Internet access TV, a Hometheater system, a smartphone, a Tablet PC, a digital video recorder(DVR) and the like.

In addition, the processing method to which the present disclosure isapplied, may be produced in the form of a program executed by acomputer, and be stored in a computer-readable recording medium.Multimedia data having a data structure according to the presentdisclosure may also be stored in a computer-readable recording medium.The computer-readable recording medium includes all kinds of storagedevices and distributed storage devices in which computer-readable dataare stored. The computer-readable recording medium may include, forexample, a Blu-ray Disc (BD), a universal serial bus (USB), a ROM, aPROM, an EPROM, an EEPROM, a RAM, a CD-ROM, a magnetic tape, a floppydisk, and an optical data storage device. Further, the computer-readablerecording medium includes media embodied in the form of a carrier wave(for example, transmission over the Internet). In addition, a bitstreamgenerated by the encoding method may be stored in a computer-readablerecording medium or transmitted through a wired or wirelesscommunication network. Additionally, the embodiments of the presentdisclosure may be embodied as a computer program product by programcodes, and the program codes may be executed on a computer by theembodiments of the present disclosure. The program codes may be storedon a computer-readable carrier.

FIG. 9 illustrates the structure of a content streaming system to whichthe present disclosure is applied.

Further, the contents streaming system to which the present disclosureis applied may largely include an encoding server, a streaming server, aweb server, a media storage, a user equipment, and a multimedia inputdevice.

The encoding server functions to compress to digital data the contentsinput from the multimedia input devices, such as the smart phone, thecamera, the camcoder and the like, to generate a bitstream, and totransmit it to the streaming server. As another example, in a case wherethe multimedia input device, such as, the smart phone, the camera, thecamcoder or the like, directly generates a bitstream, the encodingserver may be omitted. The bitstream may be generated by an encodingmethod or a bitstream generation method to which the present disclosureis applied. And the streaming server may store the bitstream temporarilyduring a process to transmit or receive the bitstream.

The streaming server transmits multimedia data to the user equipment onthe basis of a user's request through the web server, which functions asan instrument that informs a user of what service there is. When theuser requests a service which the user wants, the web server transfersthe request to the streaming server, and the streaming server transmitsmultimedia data to the user. In this regard, the contents streamingsystem may include a separate control server, and in this case, thecontrol server functions to control commands/responses betweenrespective equipments in the content streaming system.

The streaming server may receive contents from the media storage and/orthe encoding server. For example, in a case the contents are receivedfrom the encoding server, the contents may be received in real time. Inthis case, the streaming server may store the bitstream for apredetermined period of time to provide the streaming service smoothly.

For example, the user equipment may include a mobile phone, a smartphone, a laptop computer, a digital broadcasting terminal, a personaldigital assistant (PDA), a portable multimedia player (PMP), anavigation, a slate PC, a tablet PC, an ultrabook, a wearable device(e.g., a watch-type terminal (smart watch), a glass-type terminal (smartglass), a head mounted display (HMD)), a digital TV, a desktop computer,a digital signage or the like. Each of servers in the contents streamingsystem may be operated as a distributed server, and in this case, datareceived by each server may be processed in distributed manner.

Claims disclosed herein can be combined in a various way. For example,technical features of method claims of the present disclosure can becombined to be implemented or performed in an apparatus, and technicalfeatures of apparatus claims can be combined to be implemented orperformed in a method. Further, technical features of method claims andapparatus claims can be combined to be implemented or performed in anapparatus, and technical features of method claims and apparatus claimscan be combined to be implemented or performed in a method.

1. A video decoding method performed by a decoding apparatus, the methodcomprising: obtaining a bitstream including BDPCM (Block-based DeltaPulse Code Modulation) flag information; deriving residual samples for acurrent block based on the BDPCM flag information; deriving predictionsamples for the current block based on the BDPCM flag information;generating a reconstructed picture based on the residual samples and theprediction samples; deriving a boundary strength (bS) for a targetboundary of the current block in the reconstructed picture; determiningwhether deblocking filtering is applied to the target boundary based onthe bS; and performing the deblocking filtering on the reconstructedpicture based on a result of the determination, wherein the bS for thetarget boundary is derived based on the BDPCM flag information.
 2. Thevideo decoding method of claim 1, wherein the BDPCM flag information isrelated to whether a BDPCM is applied to the current block, whereinbased on the BDPCM flag information being 1, the bS for the targetboundary is derived as 0, and wherein based on the bS for the targetboundary being 0, the deblocking filtering is not applied to the targetboundary.
 3. The video decoding method of claim 2, wherein the currentblock includes a luma coding block or a chroma coding block.
 4. Thevideo decoding method of claim 3, wherein a tree type of the currentblock is a single tree type, and the current block is the chroma codingblock, and wherein based on the BDPCM flag information being 1, the bSfor the target boundary of the chroma coding block is derived as
 0. 5.The video decoding method of claim 1, wherein deriving the residualsamples includes: deriving a quantized transform coefficient for thecurrent block based on a BDPCM; and deriving a transform coefficient byperforming dequantization for the quantized transform coefficient. 6.The video decoding method of claim 5, wherein the quantized transformcoefficient is derived based on directional information for a directionin which the BDPCM is performed.
 7. The video decoding method of claim5, wherein an intra prediction sample for the current block is derivedbased on a direction in which the BDPCM is performed.
 8. A videoencoding method performed by a video encoding apparatus, the methodcomprising: deriving prediction samples for a current block based on aBDPCM (Block-based Delta Pulse Code Modulation); deriving residualsamples for the current block based on the prediction samples;generating a reconstructed picture based on the residual samples and theprediction samples; deriving a boundary strength (bS) for a targetboundary of the current block in the reconstructed picture; determiningwhether deblocking filtering is applied to the target boundary based onthe bS; performing the deblocking filtering on the reconstructed picturebased on a result of the determination; deriving quantized residualinformation based on the BDPCM; and encoding the quantized residualinformation and BDPCM flag information for the BDPCM, wherein the bS forthe target boundary is derived based on the BDPCM flag information. 9.The video encoding method of claim 8, wherein, based on the BDPCM beingapplied to the current block, the bS for the target boundary is derivedas 0, and wherein based on the bS for the target boundary being 0, thedeblocking filtering is not applied to the target boundary.
 10. Thevideo encoding method of claim 8, wherein the BDPCM flag information isrelated to whether the BDPCM is applied to the current block.
 11. Thevideo encoding method of claim 9, wherein the current block includes aluma coding block or a chroma coding block.
 12. The video encodingmethod of claim 11, wherein a tree type of the current block is a singletree type, and the current block is the chroma coding block, and whereinbased on the BDPCM being applied to the chroma coding block, the bS forthe target boundary of the chroma coding block is derived as
 0. 13. Thevideo encoding method of claim 8, wherein an intra prediction sample forthe current block is derived based on a specific direction in which theBDPCM is performed, and wherein quantization for the residual isperformed based on the specific direction.
 14. A non-transitorycomputer-readable digital storage medium storing encoded videoinformation generated by steps of: deriving prediction samples for acurrent block based on a BDPCM (Block-based Delta Pulse CodeModulation); deriving residual samples for the current block based onthe prediction samples; generating a reconstructed picture based on theresidual samples and the prediction samples; deriving a boundarystrength (bS) for a target boundary of the current block in thereconstructed picture; determining whether deblocking filtering isapplied to the target boundary based on the bS; performing thedeblocking filtering on the reconstructed picture based on a result ofthe determination; deriving quantized residual information based on theBDPCM; and encoding the quantized residual information and BDPCM flaginformation for the BDPCM, wherein the bS for the target boundary isderived based on the BDPCM flag information.
 15. A method oftransmitting data including a bitstream of video information, the methodcomprising: obtaining the bitstream of the video information includingquantized residual information and BDPCM flag information, wherein thebitstream is generated by deriving prediction samples for a currentblock based on a BDPCM (Block-based Delta Pulse Code Modulation),deriving residual samples for the current block based on the predictionsamples, generating a reconstructed picture based on the residualsamples and the prediction samples, deriving a boundary strength (bS)for a target boundary of the current block in the reconstructed picture,determining whether deblocking filtering is applied to the targetboundary based on the bS, performing the deblocking filtering on thereconstructed picture based on a result of the determination, derivingquantized residual information based on the BDPCM, and encoding thequantized residual information and the BDPCM flag information for theBDPCM; and transmitting the data comprising the bitstream of the videoinformation including the quantized residual information and the BDPCMflag information, wherein the bS for the target boundary is derivedbased on the BDPCM flag information.